Battery size: 9V; Good: 9V~7.8V; Low power: 7.7V~6V; Replace: Below: 6V. 1.BT-168D Digital Battery Tester. Battery Series. Battery size: 1.5V; Good: 1.5V~1.28V; Low power: 1.27V~1.15V; Replace: Below: 1.15V.
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